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Author Topic: GPS performance and voltage regulation  (Read 2702 times)
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Giza, Egypt
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Hi everybody, i am working on a project in which i use a GPS module (Ublox). I have a problem, when i leave the module in an open area to lock, it takes relatively long time, and when it locks, the readings i get are pretty noisy, i mean it gives positions around its original position with big error (may reach 100 meters or even more). I suspect the reason for this is the voltage supply. I use a LM7805 voltage regulator, and a 8V battery. I didn't put any capacitors on the output or input of the voltage regulator, but i'm not sure this is the problem. My question is, should this make any difference (putting capacitors on regulators) ??
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Hassan Ali
Aerospace senior student

Vienna (AT)
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Hi!

1.
You should _allways_ use capacitors with the LM7805, take a look at the datasheet (section: typical applications): 0.33µF on input and 0.1µF on output. Otherwise the voltage may oscillate.

2.
Are you sure your battery has 8 volts all the time? I think 8 volts may be not very common...
The LM7805 has a drop voltage of 2 volts (or maybe more), so with 8 volts (maybe it is only 7.2 or 7.4 volts) you are very close to the minimum input voltage and you may not get 5 volts at the output.

3.
The 78xx is not the best choice for battery powered devices, as it needs several mA even without load. There may be better regulators.
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Most GPS modules require 3.3V for power, including ublox ones. LM7805 gives 5V regulated output. Hope you didn't burnt that GPS module.
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